There are a number of medicament delivery devices on the market that are intended for self-administration. These devices have different degrees of functionality and thus complexity both regarding number of interacting components and handling of the actual device for delivering a dose of medicament.
In order that the patient or user is alerted regarding the state of the device for example regarding the number of doses that have been delivered or are remaining as well as the dose size, if the user may set different dose sizes, some devices are arranged with indicia visible through openings or windows in the device for mechanical dose information mechanisms or electronic displays if the device is provided with electronic dose information mechanisms.
Regarding mechanical dose information mechanisms, indicia are often arranged on an outer surface of a rotatingly arranged member, which during dose setting and/or dose delivery rotates a certain amount, which is displayed in the opening or window of the device. This function is adequate for many devices where the doses are rather large and/or that the rotation of the dose information member is to such an extent that all the indicia to be shown can fit onto the surface of the member.
However, for some devices and in particular when the dose increments are rather small, or the movement of the indicia member is rather small for a set dose, all indicia to be shown cannot fit onto the surface of the member which leads to problem regarding providing the user with the appropriate information.
There is thus a need for improvement regarding mechanical dose information mechanisms that also can handle small dose increments such that the proper information is provided to the user, e.g. having some sort of transmission or the like in order to handle movement of components of a medicament delivery device.
U.S. Pat. No. 6,004,297 discloses an injection syringe comprising a housing, a piston rod with a non-circular cross-section and an outer thread, a piston rod drive which includes a piston rod guide mating with the cross-section of the piston rod, and a nut which is not axially displaceable and which mates with the thread of the piston rod to form a self-locking thread connection.
Rotation of a dose setting element causes an injection button to be screwed out to project from the housing. When the injection button is pushed axially, such axial movement is transformed, by way of the threaded coupling, into a rotation of one of the piston drive elements relative to the other one. A unidirectional coupling between the nut member and the piston rod guide allows rotation in one direction by which the piston rod is transported in a distal direction. The coupling has an initial reluctance to be overcome before rotation takes place, said reluctance being large enough to resist torques exerted during the dose setting.
U.S. 2008/287,883 discloses an injection device for apportioning set doses of a drug from a reservoir to a subject. The injection device comprises a housing having an interior thread formed as an outwardly pointing thread carried on an upstanding tower centrally located in the pen shaped device. This outwardly pointing thread forms a first thread connection with the interior thread of the rotatable scale drum. The injection device further comprises a driver for moving the piston rod forward when moved axially. The driver operates the piston rod through a second thread connection having a pitch different than the first thread connection.
Non of the documents do however address the problem with displaying dose information in connection with mechanical devices for all types of dose sizes and dose increments.